Amazon aims for carbon-neutral by 2030

Amazon.com announced it will disclose its carbon footprint later this year, giving consumers and investors new insight into the environmental cost of its popular two-day shipping. The company also pledged in a blog post Monday that half its shipments would be 'net zero” carbon - also known as carbon-neutral - by 2030.

The world's biggest e-commerce company has for years resisted pressure from investors and other stakeholders to disclose more information about its environmental impact.

Late last year, several Amazon employees used their stock grants to submit shareholder proposals asking the company to devise and disclose its plans for climate change.

Estimating the emissions from e-commerce is complicated. Ordering something online often is less energy intensive than driving to and from a physical store to pick up an item because shipping can take advantage of economies of scale.

But the benefit declines rapidly as delivery times get shorter and when customers don't group items together, said Josué Velázquez-Martínez, a sustainable logistics professor at MIT.

That's a challenge for Amazon, which now counts more than 100 million Prime members, all of whom are eligible for two-day shipping.

'When customers want to receive a product in one or two days, the carbon emissions increase substantially,” he said. 'If you are willing to wait a week, it's like killing just 20 trees instead of 100 trees.”